When the oxidation number of an element decreases over the course of a reaction, that element has beenWhich of the following chemical reactions is an oxidation-reduction reaction?
CuSO4 + BaCl2 yields BaSO4 + CuCl2

AgNO3 + NaCl yields AgCl + NaNO3

Pb(NO3)2 + 2NaCl yields PbCl2 + 2NaNO3

Zn + H2SO4 yields ZnSO4 + H2